1. Technical Field
The invention relates to the construction of electrochemical cells for removal of metals from solutions, for example, to remove harmful metals from wastes to make the waste environmentally acceptable for disposal and to recover valuable metals from solutions.
2. Background Art
A number of electrochemical cells are known for recovery of metals from generally dilute solutions such as waste water or other effluents by means of electrodeposition of the metals from the solutions. Such a cell is disclosed for example in U.S. Pat. No. 5,690,806 of Sunderland et al. This cell includes an outer tubular casing that houses a cathode assembly in the form of a cylindrically shaped carbon fiber material wrapped about a mesh tubular support of generally open structure. A long current feeder running the length of the tubular support provides current to the carbon fiber cathode. The cathode assembly is surrounded by a concentric tubular anode spaced from the cathode. The electrolyte solution from which the metal is to be removed is introduced into the cell through an inlet and flows along a flow path carrying it through the porous carbon fiber cathode to an outlet while the metals of concern are deposited on the surfaces of the carbon fibers making up the cathode.
In general, in such cells, the maximum current density is usually limited by the ionic depletion of the electrolyte immediately adjacent the surface of the electrode on which material is deposited. In the cell of U.S. Pat. No. 5,690,806, for example, the porous carbon fiber cathode presents a greatly increased surface area in a generally efficient configuration for removal of metallic ions from the electrolyte solution. Notwithstanding the improved efficiency and performance of this cell, certain practical improvements remain to be needed for efficient high-volume industrial use. The present invention provides certain practical improvements in the cell of the aforementioned U.S. Pat. No. 5,690,806.